1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus to form images on long sheets.
2. Description of Related Art
In a typical image forming apparatus using electrophotography, uniformly-charged photoreceptors are irradiated with (exposed to) laser light based on image data and thus electrostatic latent images are formed on the surfaces of the photoreceptors. Toners are then supplied onto the photoreceptors on which the electrostatic latent images have been formed. This process visualizes the electrostatic latent images to form toner images. The toner images are transferred onto a sheet directly or indirectly through an intermediate transfer member, and then the transferred toner images are heated and pressurized at a fixing unit. An image is thus formed on the sheet.
Unfortunately, such an image forming apparatus gives damages to sheets (e.g., deformation and discoloration of sheets and image defects on sheets) due to the heat from the fixing unit.
Japanese Unexamined Patent Application Publication No. 2010-79086 discloses an image forming apparatus that adjusts the temperature of a pressure member constituting a fixing unit to a predetermined scope to reduce image defects on sheets.
In a case in which a sheet used for image formation is a long sheet, such as roll paper, to extend from the sheet feed opening to the sheet output opening of an image forming apparatus body, the long sheet needs to be disposed through the image forming apparatus body to extend from the sheet feed opening to the sheet output opening before the image formation, so that the long sheet can be wound adjacent to the sheet output opening (printing preparation). If the long sheet is conveyed into the fixing unit while the fixing unit is at a temperature at which the fixing unit can actually perform fixation, the front edge of the long sheet may be wound around the fixing unit or discoloration and deformation of the long sheet may be caused because the fixing unit continues to transfer heat to the long sheet staying in the fixing unit during the time from completion of the printing preparation to the start of the image formation.